HOLYOKE — An accident on Interstate 91 involving five cars Monday night caused a traffic tie-up in the southbound lanes and sent a woman to the hospital as a precaution, Massachusetts State Police said.

The accident was reported just before 6 p.m. along the section of the highway just south of the Oxbow and near the Mount Tom power plant on Route 5, said Trooper Reid Bagley.

The collision blocked one of the two travel lanes and caused "a fairly significant backup," Bagley said. Traffic was already heavy with people returning from a 3-day weekend, he said.

Northampton fire and ambulance responded to the scene.

A 33-year-old Springfield woman was taken by ambulance to Baystate Medical Center in Springfield. Bagley said she did not appear to be injured, but she was taken to the hospital as a precaution, he said.

It took about an hour to clear the scene and get traffic flowing again, he said.